BIOL 2311 Lecture Notes - Lecture 9: Inositol, Steroid Hormone Receptor, Adenylyl Cyclase
CH 9 cell communications
Cells communicate with one another in three ways:
Direct contact:
- cytoplasm of adjacent cells are connected. molecules on surface of one cell are recognized by
receptors of adjacent cell. This signal molecule will transfer into the target cell until a final cellular
response.
-In animal cells, gap junctions synchronize metabolic activities of electrical signals btwn cells in a tissue.
-In plant cells, direct channels of communication are plasmodesmata.
-cell to cell recognition, animal cells w/ particular membrane bound cell surface molecules dock w/ one
another
Local signaling:
-a secreting cell releases a signaling molecule that diffuses through the extracellular fluid and causes a
response in nearby target cells.
-Paracrine signaling – is communication across as synapse- the communicating
connection btwn neurons. signal released from a cell has an effect on neighboring cells.
1. Synaptic signaling: nerve cells release the signal (neurotransmitter) which binds to receptors
nearby cells.
2. Chemical synapse
Long-distance signaling,
-sometimes target cells far way so a medium used to transfer the signals.
-A controlling cell secretes a long distance signaling molecule called a hormone, which produces a
response in target cells tht may be far away.
- Endocrine signaling – hormones released from a cell affect other cells throughout the body. Ex:
hormones.
Target cells process the signal in three sequential steps:
Reception: binding of a signal molecule with a specific receptor on a target cell
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-Receptors for polar signal molecules (such as epinephrine) have a binding site for the signal molecule
on the cell surface
-Receptors for nonpolar signal molecules (such as steroid hormones) are located within the cell.
Transduction: encoding. changes a signal into a form that causes a cellular response.
-The initial signal binds to and activates the receptor, changing it to a form that typically initiates a
signaling cascade- a sequence of reactions tht include several diff molecules.
- Both proteins and second messengers can be part of the signaling cascade that results in triggering a
cellular response.
cellular Response: a response to the transduction. In the Sutherland's work, response was the
activation of the enzyme glycogen phosphorylase. Catalyzes the conversion on stored glycogen to
glucose which is the response to the signal delivered by epinephrine.
Communication between cells requires:
-ligand: the signaling molecule
-receptor protein: the molecule to which the signal binds - may be on the plasma membrane or within
the cell.
Cell communication:
A cell’s response to a signal often involves activating or inactivating proteins.
-Phosphorylation is a common way to change the conformation and activity of a protein.
Can be active or inactive based on the protein and the transduction pathway.
protein kinase – an enzyme that adds a phosphate to a protein
phosphatase – an enzyme that removes a phosphate from a protein
Receptor types:
Receptors can be defined by their location.
intracellular receptor – located within the cell
cell surface receptor or membrane receptor – (are integral membrane glycoprotein) located on the
plasma membrane to bind a ligand outside the cell.
Receptor proteins:
Receptor proteins have a three-dimensional shape that fits a specific signal molecule.
When a signal molecule and receptor protein bind, a change in the receptor protein is induced and a
response in the cell is generated.
A particular receptor binds only one type of signal molecule or a closely related group of signal
molecules
There is a conformational change that arises from the ligand binding to the receptor
Receptor-ligand complex can directly or indirectly interact with a whole host of other signaling
molecules within the cell
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Surface receptors:
Diff cells have diff receptor types tht are not fixed, change as cell develops. Changes also occur as
normal cells are transformed into cancer cells.
A signaling molecule binds to a surface receptor and changes the receptor's conformation so tht signal
is sent thru plasma membrane. This activates the cytoplasmic end of the receptor. The activated
receptor then initiates the first step in a cascade of molecular events—the signaling cascade—that
triggers the cellular response.
Cell surface receptors:
There are 3 subclasses of membrane receptors:
1. channel linked receptors – ion channel that opens in response to a ligand
2. enzymatic receptors – receptor is an enzyme that is activated by the ligand (receptor tyrosine+
Kinases)
3. G protein-coupled receptor – a G-protein (bound to GDP/GTP) assists in transmitting the signal.
Anchored to the membrane.
G proteins:
Two types - Ras and Trimeric G protein
Ras is monomeric
Trimeric has 3 subunits – alpha, beta and gamma
Both of them bind GTP in their active form and bind GDP in their inactive
form
The guanine nucleotide binds to the alpha subunit in the trimeric protein
G-protein coupled receptors:
G-protein-coupled receptor (GPCRs) – receptors bound to G proteins
-GPCRs lack built-in protein kinase activity.
-These receptors have seven transmembrane α-helical segments that zigzag across the
plasma membrane. Binding of a signaling molecule at the cell surface, by inducing changes
in the positions of some of the helices, activates the cytoplasmic end of the receptor.
- G-protein is a switch turned on by the receptor, the extracellular signaling molecule is called the
first messenger which binds to the receptor and activates it.
- activated receptor activates the G-protein then activates an effector protein (usually an enzyme)
-Once activated, the effector protein produces one or more internal, nonprotein signaling molecules
called second messengers, which results in the activation of protein kinases.
-These kinases phosphorylate specific target proteins, thereby eliciting the cellular response.
- So second messenger generates the cellular response to the original signal.
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Document Summary
Cells communicate with one another in three ways: Cytoplasm of adjacent cells are connected. molecules on surface of one cell are recognized by receptors of adjacent cell. This signal molecule will transfer into the target cell until a final cellular response. In animal cells, gap junctions synchronize metabolic activities of electrical signals btwn cells in a tissue. In plant cells, direct channels of communication are plasmodesmata. Cell to cell recognition, animal cells w/ particular membrane bound cell surface molecules dock w/ one another. A secreting cell releases a signaling molecule that diffuses through the extracellular fluid and causes a response in nearby target cells. Sometimes target cells far way so a medium used to transfer the signals. A controlling cell secretes a long distance signaling molecule called a hormone, which produces a response in target cells tht may be far away. Endocrine signaling hormones released from a cell affect other cells throughout the body.
